Fluorescent lamp igniting circuit

ABSTRACT

A transistor is between, and in series with, the heating filaments of a fluorescent lamp, to allow current flow therethrough when power is initially applied to the circuit. A predetermined time after power is applied to the circuit, determined either by the time required to charge a capacitor to a predetermined potential or by the time required to increase the impedance of one of the heating filaments to a predetermined impedance as a result of heating caused by I2R losses, the transistor is rendered nonconductive. When the transistor is rendered nonconductive an induction coil, in series with the filaments, provides a momentary additive transient voltage to ignite the lamp.

United States Patent 1 1 Kahanic l 1March 13, 1973 [75] Inventor:Francis P. Kahanic, Arlington Heights, 111. [73] Assignee: TeletypeCorporation, Skokie, 111.

[22] Filed: Dec. 21, 1970 [21] Appl. No.: 99,934

[52] U.S.Cl. ..315/l01,315/l02,315/107,

315/307, 315/310, 307/305 [51] Int. Cl. ..H05b 37/00, H05b 41/14 [58]Field of Search ..315/99,101,102,103,107, 315/100 U, 307, 310; 307/885,305, 252 J,

3,505,562 4/1970 Engel ..315/99 X 3,165,668 1/1965 Hardley ..315/307 X3,265,930 8/1966 Powell, Jr. ..315/100 U Primary Examinerl-lerman KarlSaalbach Assistant Examiner-Saxfield Chatmon, Jr. Attorney-J. L. Landisand R. P. Miller 571 ABSTRACT A transistor is between, and in serieswith, the heating filaments of a fluorescent lamp, to allow current flowtherethrough when power is initially applied to the circuit. Apredetermined time after power is applied to the circuit, determinedeither by the time required to charge a capacitor to a predeterminedpotential or by the time required to increase the impedance of one ofthe heating filaments to a predetermined impedance as a result ofheating caused by PR losses, the transistor is rendered nonconductive.When the transistor is rendered nonconductive an induction coil, inseries with the filaments, provides a momentary additive transientvoltage to ignite the lamp.

14 Claims, 3 Drawing Figures PATENTEDHAR 1 3 I973 3 720.861

=.- |8 FRANCIS P. KAHANIC v BY ATTORNEY FLUORESCENT LAMP IGNITINGCIRCUIT BACKGROUND OF THE INVENTION The present invention relates tofluorescent lamp ignition circuits, and in particular to circuitsemploying semiconductive devices to ignite a fluorescent lamp.

In igniting fluorescent lamps having heating filaments, there is a needfor circuitry to provide ignition when the heating filaments are at theproper temperature to support ignition of the lamp. If ignition isprovided before the filaments are at the proper temperature, the lampwill be unable to sustain the ignition; while if ignition is providedwhen the temperature of the filaments has risen above the propertemperature, the filaments will have reduced life.

An object of the invention is to provide fluorescent lamp ignitioncircuitry wherein ignition is provided to the lamp when the heatingfilaments reach the proper temperature to allow the lamp to sustainignition.

SUMMARY OF THE INVENTION The foregoing and other objects of theinvention are accomplished by providing means for applying a firstpotential to a first terminal of a first filament of a fluorescent lamp,the lamp having both first and second electrically conductive filamentswith each filament having a first and a second terminal, and a secondpotential to the first terminal of the second filament. A firsttransistor switching device is connected between the second terminal ofthe first filament and the second terminal of the second filament, andis responsive to the application of the first and the second potentialsto become conductive. Second and third means are provided, the secondmeans being responsive to the application of the first and the secondpotentials to render the first semiconductive device nonconductive apredetermined time after the application of the potentials, and thethird means being responsive to the transistor switching device beingrendered nonconductive to ignite the fluorescent lamp.

Preferrably, an induction coil is provided in series with the twofilaments of the lamp, and with the transistor switching device, toprovide a momentary additive transient voltage, or inductive voltagekick, to ignite the lamp when the transistor switching device isrendered nonconductive. The conduction of the transistor switchingdevice is determined by a silicon controlled rectifier connected to thebase of the transistor, such that when the silicon controlled rectifieris conducting the transistor is rendered nonconductive, and when thesilicon controlled rectifier is nonconductive the transistor is renderedconductive. The conduction of the silicon controlled rectifier is inturn controlled by other semiconductor means.

Other objects, advantages and features of the invention will be apparentfrom the following detailed description of the specific embodimentsthereof, when taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a circuit diagram of a firstembodiment of the invention.

FIG. 2 is a circuit diagram ,of a second embodiment of the invention.

FIG. 3 is a circuit diagram of a third embodiment of the invention.

DETAILED DESCRIPTION Referring to FIGS. 1 through 3 of the drawings,there are shown three embodiments of a fluorescent lamp ignition circuitfor igniting a fluorescent lamp 11 having two heater filaments 12 and13. In each of the embodiments a resistor 14 and an induction coil 16are connected in series between an input to the heater filament 12 and asource of positive potential 17, while an input to the heater filament13 is connected directly to a source of ground potential. When a currentflow from the source of positive potential 17, through the inductioncoil 16, the resistor 14 and the heater filaments 12 and 13 to thesource of ground potential 18 is interrupted, as will be describedlater, the induction coil 16 provides a momentary inductive voltage kickto ignite the fluorescent lamp 11. In the description of the operationof the circuit shown in the drawings, reference will be made to positiveand to ground potential. These terms for defining the potentials used inthe circuit are relative terms used to illustrate the operation of thecircuit and are not to be considered limiting, since any other twopotentials could be used, the potential being substituted for thepositive potential referred to in the specification being merely morepositive than the potential being substituted for the ground potential.

FIRST EMBODIMENT The embodiment of the fluorescent lamp ignition circuitshown in FIG. 1 of the drawings also includes a resistor 21 connectedbetween the heater filament 12 and the collector of a transistor 22, theemitter of the transistor 22 being connected to the heater filament 13,so that when the transistor 22 is rendered conductive a series circuitis established from the source of positive potential 17, through theinduction coil 16, the resistor 14, the heater filament 12, the resistor21, the transistor 22 and the heater filament 13 to the source of groundpotential 18. The base of the transistor 22 is connected both to thesource of positive potential 17, through a resistor 23, and to the anodeof a silicon-controlled-rectifier 24, the cathode of thesilicon-controlled-rectifier 24 being connected to the source of groundpotential 18. The gate of the silicon controlled rectifier 24 isconnected to the anode of a Zener diode 26, the cathode of which isconnected to the emitter of the transistor 22, and therefore to theheating filament 13.

When the potentials 17 and 18 are initially applied to the circuit, thetransistor 22 is rendered conductive by the application of the positivepotential 17 at its base through the resistor 23, establishing a currentflow through the series connected elements, as recited above, comprisingthe induction coil 16, the resistor 14, the heating filament 12, theresistor 21, the transistor 22 and the heating filament 13. As a resultof the current flow through the heating filaments 12 and 13, thetemperature of the heating filaments 12 and 13 increases from PR lossestherein, causing an increase in the impedance of the filaments 12 and 13which is commensurate with the rise in the temperature of the filaments,the filaments l2 and 13 being of a conventional type having a positivetemperature coefficient of resistivity. As the impedance of thefilaments 12 and 13 increases with the rise in temperature, the voltageat a junction point 27, defined by the juncture of the emitter of thetransistor 22, the heating filament 13, and the cathode of the Zenerdiode 26, increases as a result of a voltage divider effect.

The potential at the junction point 27, when the potentials 17 and 18are initially applied to the circuit,

is below the breakdown voltage of the Zener diode 26,

the anode of which is tied at the ground potential 18 through the gateof the silicon-controllED-rectifier 24, and therefore the Zener diode 26initially remains nonconductive. As the temperatures of the heatingfilaments 12 and 13 continues to rise as a result of the R lossestherein, the voltage at the junction point 27 continues to increaseuntil the breakdown voltage of the Zener diode 26 is exceeded, causingthe Zener diode 26 to conduct and to trigger thesilicon-controlledrectifier 24, which in turn carries the groundpotential 18 to the base of the transistor 22, thereby rendering thetransistor 22 nonconductive and disrupting the current flow through thepath established by the induction coil 16, the resistor 14, the heatingfilament 12, the resister 21, the transistor 22 and the heating filament13. Disruption of the current flow through the induction coil 16 causesthe induction coil to provide an inductive voltage kick therefrom whichis applied to the fila ment12 of the lamp 11, thereby igniting the lamp11 as a result of the ionization of the gases therein caused by thelarge potential difference between the heating filaments l2 and 13. Theresulting current flowing through the induction coil 16, the resistor14, and the heating filaments 12 and 13 is sufficient to maintainignition of the lamp. I

It is to be noted that the potential at the junction point 27 when thesources of potentials 17 and 18 are initially applied to the circuit isa function of the effective impedance of the induction coil 16, theresistors 14 and 21, and the heating filaments 12 and 13; and that risein potential at the junction point 27 as a result of a voltage dividereffect is a function of the effective increase in impedance of theheating filaments 12 and 13 resulting from PR losses therein. Therefore,ignition of the lamp 11 can be made to occur when the heating filaments12 and 13 are at any desired temperature by adjusting the values of theresistors 14 and 21 to provide the breakdown potential of the Zenerdiode 26 at the junction point 27 when the heating filaments 12 and 13have reached the desired temperature. It is understood, of course, thatthe potential at the junction point 27 required to ignite the lamp 11may also be determined by choosing a Zener diode 26 having the requiredbreakdown voltage.

SECOND EMBODIMENT The embodiment of the fluorescent lamp ignitioncircuit shown in FIG. 2 of the drawings is substantially identical inconfiguration and operation with the circuit shown in FIG. 1, thedifference being in that a transistor 36 has replaced the Zener diode 26of FIG. 1, and in that two series connected resistors 38 and 39 havebeen connected between the two sources of potential 17 and 18 to providean input to the base of the transistor 36 from their juncture. Theemitter of the transistor 36 is connected to a junction point 37, whichis common with the emitter of a transistor 32 and the heating filament13, and the collector of the transistor 36 has been connected to thegate of a silicon-conv trolled-rectifier 34.

. described above for the circuit of FIG. 1, the emitterbase voltage ofthe transistor 36 eventually becomes sufficient to allow the transistor36 to conduct and to trigger the silicon-controlled-rectifier 34.Conduction of the silicon-controlled-rectifier 34 carries the groundpotential 18 to the base of the transistor 32, thereby rendering thetransistor 32 nonconductive and providing an inductive voltage kick fromthe induction coil.16 to ignite the lamp 11 as described above.

It is to be noted that the fluorescent lamp 1] is ignited when thetransistor 36 is rendered conductive, which occurs when the potential atthe junction 37 is equal to the potential existing at the juncturebetween the resistors 38 and 39. Therefore, ignition of the fluorescentlamp 11 may be provided when the heating filaments 12 and 13 are at anydesired temperature by adjusting the value of the resistors 14 or 31 tocontrol the potential at the junction point 37 when the heatingfilaments 12 and 13 are at the desired temperature, or by adjusting thevalues of the resistors 38 and 39 so that potential at their jucture isequal to the potential at the junction point 37 when the heatingfilaments l2 and 13 are at the desired temperature. It is to be furthernoted that, as with the circuit of FIG. 1, ignition of the lamp 11 isprovided only when the heating filaments 12 and 13 are at a desired, oroptimum, temperature, to assure a reliable and spontaneous ignition ofthe lamp.

THIRD EMBODIMENT The embodiment of the circuit shown in FIG. 3 of thedrawings includes a transistor 42, connected as a shunt between theheating filaments 12 and 13, and a series connected resistor 43 asilicon-controlled-rectifier 44 connected between the source of positivepotential 17 and the source of ground potential 18 such that the cathodeof the silicon-controlled-rectifier 44 is connected to the source ofground potential. An input is provided to the base of the transistor 42from the anode of the silicon-controlled-rectifier 44. Also connected inseries and between the sources of positive and ground potential is aresistor-capacitor network comprised of a resistor 46 and a capacitor47, such that the capacitor 47 is connected to the source of groundpotential. A Zener diode 48 is connected between the gate of thesilicon-controlled-rectifier 44 and the juncture between the resistor 46and the capacitor 47, the

cathode of the Zener diode 48 being connected to the juncture betweenthe resistor 46 and the capacitor 47.

A resistor 49 is connected between the anode of the Zener diode 48 andthe source of ground potential 18.

When the potentials 17 and 18 are initially applied to the circuit, acurrent flow is established through the.

heating filaments l2 and 13, as described for the embodiments of thecircuits shown in FIGS. 1 and 2, through the series circuit comprisingthe resistor 14, the induction coil 16, the heating filament 12, thetransistor 42 and the heating filament 13, providing for an increase intemperature of the heating filaments 12 and 13 through 1 R losses. Also,the potential at a junction point 51 between the resistor 46 and thecapacitor 47 begins to increase as the charge on the capacitor 47increases, the potential at the junction point 51 initially being belowthe breakdown voltage of the Zener diode 48, the anode of which is heldat a ground potential through the gate and cathode of thesilicon-controlledrectifier 44. When the voltage at the junction point51 reaches a predetermined potential, which potential is equal to thebreakdown voltage of the Zener diode 48 and is determined by the amountof time required for the heating filaments l2 and 13 to reach a desiredtemperature, the Zener diode 48 conducts and triggers thesilicon-controlled-rectifier 44, which in turn carries a groundpotential to the base of the transistor 42. The ground potential at thebase of the transistor 42 renders the transistor 42 non-conductive,providing an inductive voltage kick from the induction coil 16 to ignitethe lamp 11.

It is to be noted that in this embodiment of the circuit the ignitiontime of the circuit is not a function of the impedance of the heatingfilaments 12 and 13, but rather is a function of the R-C time constantof the resistor 46 and the capacitor 47 as as well as the breakdownvoltage of the Zener diode 48. The resistor 46, the capacitor 47 and theZener diode 48 are chosen to provide ignition upon the application of apotential to the circuit onlyafter the heating filaments l2 and 13 havehad an opportunity to reach a desirable and optimum ignitiontemperature.

While three embodiments of the invention have been described in detail,it will be obvious that various modifications may be made from thespecific details described without departing from the spirit and scopeof the inventions What is claimed is:

l. A circuit for igniting a fluorescent lamp, the lamp having a firstand a second electrically conductive filament and each filament having afirst and a second terminal, which comprises:

means for applying a first potential to the first terminal of the firstfilament and a second potential to the first terminal of the secondfilament;

a first semiconductive device, connected between the second terminal ofthe first filament and the second terminal of the second filament, andresponsive to the application of the first potential to becomeconductive to complete a path for a flow of current through thefirst andsecond filaments;

means responsive to the application of the first and the secondpotentials to render the first semiconductive device nonconductive apredetermined time after the application of the potentials to interruptthe flow of current through the first and second filaments; and

means responsive to the interruption of the current flow through'thefirst and second filaments to ignite the fluorescent lamp.

2. A circuit for igniting a fluorescent lamp, the lamp having a firstand second electrically conductive filament and each filament having afirst and a second terminal, the second filament being characterized inthat it exhibits a gradually increasing impedance as it is heated by PRlosses in response to the application of a potential thereacross, whichcomprises:

means for applying a first potential to the first terminal of the firstfilament and a second potential to the first terminal of the secondfilament;

a first semiconductive device, connected between the second terminal ofthe first filament and the second terminal of the second filament, andresponsive to the application of the first potential to becomeconductive to apply a potential across the second filament to graduallyincrease the potential at the connection between the firstsemiconductive device and the second terminal of the second filament asa result of a voltage divider effect as the second filament exhibits theincreasing impedance in response to the application of the potentialthereacross;

a second semiconductive device, connected to the connection between thefirst semiconductive device and the second terminal of the secondfilament, and responsive to a predetermined potential at the connectionto render the first semiconductive device nonconductive; and

means responsive to the first semiconductive device being renderednonconductive to ignite the fluorescent lamp.

3. A circuit as recited in claim 2, wherein: asiliconcontrolled-rectifier is connected to the first semiconductivedevice to control the conduction thereof; and

the second semiconductive device is also connected to thesilicon-controlled-rectifier to control the conduction thereof, suchthat nonconduction of the silicon-controlled-rectifier allows the firstsemiconductive device to conduct'and such that conduction of thesilicon-controlled-rectifier prevents the first semi-conductive devicefrom conducting.

4. A circuit as recited in claim 3, wherein:

the first semiconductive device is a transistor switching device, thebase of the transistor being connected to thesilicon-controlled-rectifier;

the second semiconductive device is a Zener diode having a breakdownpotential equal to the predetermined potential; and

the means for igniting the lamp includes an induction coil connected inseries with the first terminal of the first filament.

5. A circuit as recited in claim 3, further including:

first and second series connected resistors connected between the firstand the second potentials, the'resistors being of such a value that thepotential at the connection between them is equal to the predeterminedpotential; and wherein the first semiconductive device is a transistorswitching device;

the second semiconductive device is a transistor switching device, theemitter of the transistor being connected to the connection between thefirst transistor and the second terminal of the second filament and thebase of the transistor being connected to the connection between thefirst and the second resistors, so that when the potential at theemitter reaches the predetermined potential the transistor is renderedconductive to render the silicon-controlled-rectifier conductive; and

the means for igniting the lamp includes an induction coil connected inseries with the portion of the circuit including the means for applyingthe first potential and the first terminal of the first filament, sothat when the first transistor is rendered non conductive an inductivevoltage kick is provided to ignite the lamp.

6. Acircuit for igniting a fluorescent lamp, the lamp having a first anda second electrically conductive filament and each filament having afirst and a second terminal, which comprises:

means for applying a first potential to the first terminal of the firstfilament and a second potential to the first terminal of the secondfilament;

a first semiconductive device, connected between the second terminal ofthe first filament and the second terminal of the second filament, andresponsive to the application of the first potential to becomeconductive;

a resistor-capacitor network, connected in series between the means forapplying the first potential and the means for applying the secondpotential;

a second semiconductive device, connected to the connection between theresistor and the capacitor of the resistor-capacitor network for sensingthe potential on the capacitor, and responsive to a predeterminedpotential on the capacitor to render the first semiconductive devicenonconductive, the potential on the capacitor being below thepredetermined potential when the first potential is initially appliedand gradually rising to the predetermined potential in response to theapplication of the first and the second potentials; and

means responsive to the first semiconductive device being renderednonconductive to ignite the fluorescent lamp.

7. A circuit as recited in claim 6 wherein:

a silicon controlled rectifier is connected to the first semiconductivedevice to control the conduction 7 thereof; and

the second semiconductive device is connected to thesi]icon-controlled-rectifier to control the conduction thereof, suchthat nonconduction of the silicon-controlled-rectifier allows the firstsemiconductive device to conduct and such that conduction of thesilicon-controlled rectifier prevents the first semiconductive devicefrom conducting.

8. A circuit as recited in claim 7, wherein:

the first semiconductive device is a transistor switching device, thebase of the transistor being connected to thesilicon-controlled-rectifier;

the second semiconductive device is a Zener diode, the breakdownpotential of the diode being equal to the predetermined potential; and

the means for igniting the lamp includes an induction coil connected inseries with the first terminal of the first filament.

9. In a fluorescent lamp igniting circuit, the lamp having at least onefilament responsive to the application of a voltage to generate heatthrough 1 R losses, the filament exhibiting a first impedance prior tothe application of the voltage and being characterized in that itexhibits a gradually increasing impedance as its temperature increasesin response to the application of the voltage, the improvement whichcomprises:

an impedance coupled in series with the filament to form a voltagedivider;

a'transistor switching device connected in series with the impedance andthe filament to control the conduction of current therethrough; asemiconductor device for sensing the potential between the impedance andthe filament, and

responsive to the potential reaching the predetermined potential as aresult of the impedance of the filament reaching a predeterminedimpedance to render the transistor switching device nonconductive; and

means, responsive to nonconduction of the transistor switching device,to ignite the lamp.

10. A circuit as recited in claim 9, wherein:

a silicon-controlled-rectifier is connected to the base of thetransistor switching device to control the conduction thereof; and

the semiconductor device is a Zener diode connected to thesilicon-controlled-rectifier to control the conduction thereof.

1 1. A circuit as recited in claim 9, wherein:

a silicon-controlled-rectifier is connected to the base of thetransistor switching device to control the conduction thereof; and

the semiconductor device is a transistor switching device connected tothe silicon-controlled-rectifier to control the conduction thereof. I

12. A circuit for igniting a fluorescent lamp, the fluorescent lamphaving an input terminal and an output terminal, which comprises:

a resistor-capacitor network;

means for applying a voltage across the network to thereby increase thepotential at the connection between the resistor and the capacitor;

a transistor switching device, connected between the input and theoutput terminals, and responsive to the application of the voltage tobecome conductive to complete a path for a flow of current between theinput and the output terminals; means, responsive to the potentialbetween the resistor and capacitor reaching a predetermined potential,to render the transistor nonconductive to interrupt the flow of currentbetween the input and the output terminals; and 1 means, responsive tothe interruption of the flow of current between the input and the outputterminals, to ignite the lamp.

13. In a circuit for igniting a fluorescent tube having a pair of spacedfilaments that exhibit an increased impedance upon application ofcurrent therethrough;

a transistor having its collector connected to a first one of thefilaments and its emitter connected to the second one of the filaments;

means for applying operating current through the filaments and the baseof the transistor to initiate conduction therethrough;

a semiconductive device having three electrodes, one of which controlsconduction between the other two electrodes, and then relinquishescontrol of conduction between the other two electrodes;

means, responsive to a predetermined increase in impedance of thefilaments, for applying a conduction potential to the control electrodeto render conductive the semiconductive device; and

means, responsive to the conduction of the semiconductive device, tointerrupt conduction of the transistor and to generate and apply a pulseto ignite the fluorescent tube.

14. A circuit for igniting a fluorescent lamp, the fluorescent lamphaving an input terminal and an output terminal, which comprises:

a resistor-capacitor network;

means for applying a voltage across the network to thereby increase thepotential at the connection between the resistor and the capacitor;

a transistor switching device, connected between the input and theoutput terminals, and responsive to the application of the voltage tobecome conductive;

means, responsive to the potential between the resistor and capacitorreaching a predetermined potential, to render the transistornonconductive;

an inducation coil in series with the input to the lamp;

a Zener diode, having a breakdown potential equal to the predeterminedpotential, for sensing the potential at the connection between theresistor and the capacitor;

a silicon-controlled-rectifier, connected to the transistor switchingdevice to control the conduction thereof; and

means for connecting a Zener diode to the silicon-

1. A circuit for igniting a fluorescent lamp, the lamp having a firstand a second electrically conductive filament and each filament having afirst and a second terminal, which comprises: means for applying a firstpotential to the first terminal of the first filament and a secondpotential to the first terminal of the second filament; a firstsemiconductive device, connected between the second terminal of thefirst filament and the second terminal of the second filament, andresponsive to the application of the first potential to becomeconductive to complete a path for a flow of current through the firstand second filaments; means responsive to the application of the firstand the second potentials to render the first semiconductive devicenonconductive a predetermined time after the application of thepotentials to interrupt the flow of current through the first and secondfilaments; and means responsive to the interruption of the current flowthrough the first and second filaments to ignite the fluorescentlamp.
 1. A circuit for igniting a fluorescent lamp, the lamp having afirst and a second electrically conductive filament and each filamenthaving a first and a second terminal, which comprises: means forapplying a first potential to the first terminal of the first filamentand a second potential to the first terminal of the second filament; afirst semiconductive device, connected between the second terminal ofthe first filament and the second terminal of the second filament, andresponsive to the application of the first potential to becomeconductive to complete a path for a flow of current through the firstand second filaments; means responsive to the application of the firstand the second potentials to render the first semiconductive devicenonconductive a predetermined time after the application of thepotentials to interrupt the flow of current through the first and secondfilaments; and means responsive to the interruption of the current flowthrough the first and second filaments to ignite the fluorescent lamp.2. A circuit for igniting a fluorescent lamp, the lamp having a firstand second electrically conductive filament and each filament having afirst and a second terminal, the second filament being characterized inthat it exhibits a gradually increasing impedance as it is heated by I2Rlosses in response to the application of a potential thereacross, whichcomprises: means for applying a first potential to the first terminal ofthe first filament and a second potential to the first terminal of thesecond filament; a first semiconductive device, connected between thesecond terminal of the first filament and the second terminal of thesecond filament, and responsive to the application of the firstpotential to become conductive to apply a potential across the secondfilament to gradually increase the potential at the connection betweenthe first semiconductive device and the second terminal of the secondfilament as a result of a voltage divider effect as the second filamentexhibits the increasing impedance in response to the application of thepotential thereacross; a second semiconductive device, connected to theconnection between the first semiconductive device and the secondterminal of the second filament, and responsive to a predeterminedpotential at the connection to render the first semiconductive devicenonconductive; and means responsive to the first semiconductive devicebeing rendered nonconductive to ignite the fluorescent lamp.
 3. Acircuit as recited in claim 2, wherein: a silicon-controlled-rectifieris connected to the first semiconductive device to control theconduction thereof; and the second semiconductive device is alsoconnected to the silicon-controlled-rectifier to control the conductionthereof, such that nonconduction of the silicon-controlled-rectifierallows the first semiconductive device to conduct and such thatconduction of the silicon-controlled-rectifier prevents the firstsemi-conductive device from conducting.
 4. A circuit as recited in claim3, wherein: the first semiconductive device is a transistor switchingdevice, the base of the transistor being connected to thesilicon-controlled-rectifier; the Second semiconductive device is aZener diode having a breakdown potential equal to the predeterminedpotential; and the means for igniting the lamp includes an inductioncoil connected in series with the first terminal of the first filament.5. A circuit as recited in claim 3, further including: first and secondseries connected resistors connected between the first and the secondpotentials, the resistors being of such a value that the potential atthe connection between them is equal to the predetermined potential; andwherein the first semiconductive device is a transistor switchingdevice; the second semiconductive device is a transistor switchingdevice, the emitter of the transistor being connected to the connectionbetween the first transistor and the second terminal of the secondfilament and the base of the transistor being connected to theconnection between the first and the second resistors, so that when thepotential at the emitter reaches the predetermined potential thetransistor is rendered conductive to render thesilicon-controlled-rectifier conductive; and the means for igniting thelamp includes an induction coil connected in series with the portion ofthe circuit including the means for applying the first potential and thefirst terminal of the first filament, so that when the first transistoris rendered nonconductive an inductive voltage kick is provided toignite the lamp.
 6. A circuit for igniting a fluorescent lamp, the lamphaving a first and a second electrically conductive filament and eachfilament having a first and a second terminal, which comprises: meansfor applying a first potential to the first terminal of the firstfilament and a second potential to the first terminal of the secondfilament; a first semiconductive device, connected between the secondterminal of the first filament and the second terminal of the secondfilament, and responsive to the application of the first potential tobecome conductive; a resistor-capacitor network, connected in seriesbetween the means for applying the first potential and the means forapplying the second potential; a second semiconductive device, connectedto the connection between the resistor and the capacitor of theresistor-capacitor network for sensing the potential on the capacitor,and responsive to a predetermined potential on the capacitor to renderthe first semiconductive device nonconductive, the potential on thecapacitor being below the predetermined potential when the firstpotential is initially applied and gradually rising to the predeterminedpotential in response to the application of the first and the secondpotentials; and means responsive to the first semiconductive devicebeing rendered nonconductive to ignite the fluorescent lamp.
 7. Acircuit as recited in claim 6 wherein: a silicon controlled rectifier isconnected to the first semiconductive device to control the conductionthereof; and the second semiconductive device is connected to thesilicon-controlled-rectifier to control the conduction thereof, suchthat nonconduction of the silicon-controlled-rectifier allows the firstsemiconductive device to conduct and such that conduction of thesilicon-controlled rectifier prevents the first semiconductive devicefrom conducting.
 8. A circuit as recited in claim 7, wherein: the firstsemiconductive device is a transistor switching device, the base of thetransistor being connected to the silicon-controlled-rectifier; thesecond semiconductive device is a Zener diode, the breakdown potentialof the diode being equal to the predetermined potential; and the meansfor igniting the lamp includes an induction coil connected in serieswith the first terminal of the first filament.
 9. In a fluorescent lampigniting circuit, the lamp having at least one filament responsive tothe application of a voltage to generate heat through I2R losses, thefilament exhibiting a first impedance prIor to the application of thevoltage and being characterized in that it exhibits a graduallyincreasing impedance as its temperature increases in response to theapplication of the voltage, the improvement which comprises: animpedance coupled in series with the filament to form a voltage divider;a transistor switching device connected in series with the impedance andthe filament to control the conduction of current therethrough; asemiconductor device for sensing the potential between the impedance andthe filament, and responsive to the potential reaching the predeterminedpotential as a result of the impedance of the filament reaching apredetermined impedance to render the transistor switching devicenonconductive; and means, responsive to nonconduction of the transistorswitching device, to ignite the lamp.
 10. A circuit as recited in claim9, wherein: a silicon-controlled-rectifier is connected to the base ofthe transistor switching device to control the conduction thereof; andthe semiconductor device is a Zener diode connected to thesilicon-controlled-rectifier to control the conduction thereof.
 11. Acircuit as recited in claim 9, wherein: a silicon-controlled-rectifieris connected to the base of the transistor switching device to controlthe conduction thereof; and the semiconductor device is a transistorswitching device connected to the silicon-controlled-rectifier tocontrol the conduction thereof.
 12. A circuit for igniting a fluorescentlamp, the fluorescent lamp having an input terminal and an outputterminal, which comprises: a resistor-capacitor network; means forapplying a voltage across the network to thereby increase the potentialat the connection between the resistor and the capacitor; a transistorswitching device, connected between the input and the output terminals,and responsive to the application of the voltage to become conductive tocomplete a path for a flow of current between the input and the outputterminals; means, responsive to the potential between the resistor andcapacitor reaching a predetermined potential, to render the transistornonconductive to interrupt the flow of current between the input and theoutput terminals; and means, responsive to the interruption of the flowof current between the input and the output terminals, to ignite thelamp.
 13. In a circuit for igniting a fluorescent tube having a pair ofspaced filaments that exhibit an increased impedance upon application ofcurrent therethrough; a transistor having its collector connected to afirst one of the filaments and its emitter connected to the second oneof the filaments; means for applying operating current through thefilaments and the base of the transistor to initiate conductiontherethrough; a semiconductive device having three electrodes, one ofwhich controls conduction between the other two electrodes, and thenrelinquishes control of conduction between the other two electrodes;means, responsive to a predetermined increase in impedance of thefilaments, for applying a conduction potential to the control electrodeto render conductive the semiconductive device; and means, responsive tothe conduction of the semiconductive device, to interrupt conduction ofthe transistor and to generate and apply a pulse to ignite thefluorescent tube.